1. Field of the Invention
The present invention relates to bearing devices such as dynamic pressure bearings and slide bearings.
2. Description of the Prior Art
In bearing devices such as a dynamic pressure bearings and the like, having a plurality of bearing portions, their bearing performance significantly depends on the concentricity between inner and outer diameters of each bearing portion as well as on the alignment of the plurality of bearing portions. If any misalignment takes place in setting up the bearing portions, the resulting performance would be quite low. Accordingly, to attain successful bearing performance, the machining of the bearing portions must be carried out at very high precision, which may cause a problem of increased prices of the bearing devices.
This being the case, there has been provided a dynamic pressure bearing as shown in FIG. 5, intended to solve the foregoing problem. To provide this dynamic pressure bearing, a plurality of bearing portions 32 and 35 are integrally molded with a sleeve 31, so that the concentricity and alignment of the plurality of bearing portions 32 and 35 can readily be ensured. The dynamic pressure bearing mentioned above, having a very small clearance between the bearing portions 32 and 35 and a shaft (not shown) fitted thereto, is required to suppress the friction torque of grease between the sleeve 31 and the shaft. To do this, there is provided a concave portion 33 in the center of the inner periphery of the sleeve 31 at a portion other than the bearing portions 32 and 35, thereby giving a larger clearance between the concave portion 33 and the shaft. However, the process of forming the concave portion 33 in the center portion of the inner periphery of the sleeve 31 is difficult. Another difficulty arises in washing the concave portion 33.